Exemplary embodiments of the invention relate to a rotary wing aircraft, and more particularly, to a system and method for reducing vibrations generated by a main rotor hub of a rotary wing aircraft.
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. While vibration in a given system is occasionally desirable, it is more often undesirable due to the tendency of vibrations to waste energy, create noise and have deleterious effects on mission performance. In aircraft operations, such as single-rotor helicopters or helicopters with coaxial, counter-rotating main rotors, vibrations may be cause by normal rotor operation. These vibrations as well as other types of vibrations (e.g., those caused by damage) are transmitted to the airframe and can lead to uncomfortable flight conditions or damage. Thus, it is often required that at least a portion of the generated vibrations be mitigated or reduced.
Conventional vibration reduction systems use fixed weights mounted to each of the rotor blades to provide a damping at a first frequency. In addition, weights are positioned about the center of rotation of a main rotor system and are designed to rotate with the rotor system to effectively interfere with and mitigate the vibrations. The weights mounted to the rotor hub are intended to mitigate vibrations at the same first frequency. The fixed weights mounted to the rotor blades are intended to provide coarse adjustment at a rotor blade lever and the weights mounted to the rotor hub provide fine adjustment at the aircraft level. However, these current systems are time consuming to install and the balancing of the rotor blades may only occur when the aircraft is grounded.